Specific heat of kagomé ice in the pyrochlore oxide Dy ₂Ti₂O₇

A novel macroscopically degenerate state called kagomé ice, which was recently found in a spin ice compound Dy₂Ti₂O ₇ in a magnetic field applied along the [111] direction of the cubic unit cell, is studied by specific heat measurements. The residual entropy of the kagomé ice is estimated to be 0.65 J/K mol Dy, which is nearly 40% of that for the tetrahedral spin ice obtained in a zero field (1.68 J/K mol Dy) and is in good agreement with a theoretical prediction. It is also reported that the kagomé ice state, which is stabilized at a range of magnetic field of 0.3-0.6 T, is a "gas" phase and condenses into a "liquid" phase with nearly zero entropy at a critical field of 1 T.